Clutches are an important component of automobiles such as trucks, buses, cars etc. Typically clutches are the devices adapted to connect a driven means and a rotational power source. The clutch assembly is generally fitted on a flywheel, which is mounted on, and rotatable with, a driving shaft such as the crankshaft of the internal combustion engine. One or more pressure plates are fixed to the clutch assembly for rotation with it, while being displaceable axially under the biasing action of axially acting clutch engaging means controlled by declutching means. One or more friction disc, carrying at least one friction liner at its outer periphery, and being fixed to and rotatable with a driven shaft such as the input shaft of the gearbox, is interposed between the pressure plate and the flywheel so as to be gripped between them when the clutch is in its engaged condition. The clutch engaging means control the axial displacement of the pressure plate when they are actuated by a clutch release bearing through the declutching means.
In the course of the working of such a clutch, the friction liner or liners and the components with which they cooperate, namely the pressure plate and flywheel become worn out. The worn out condition of the component causes variation in the position of the pressure plate, the axially acting clutch engaging means and the clutch release bearing. Such a change in position affects the working condition of the declutching means. Also such a change in the position will alter the effect of biasing members placed between the clutch cover and pressure plate. Hence it is required to bring back or restore this change or at least restore the position of axially acting clutch engaging means and the clutch release bearing.
Generally clutches have the provision of adjustment for the position of the release bearing to pay off for the wear. Typically a wear take-up assembly is often used to do the manual adjustment. The wear take-up assembly has an adjusting ring and a clutch adjuster. The adjusting ring is disposed circumferentially and has teeth along its inner circumference. The teeth being adapted to cooperate with the clutch adjuster. Manual rotation of the clutch adjuster causes rotation of the adjusting ring relative to clutch cover thereby causing a change in the position of release bearing.
One such arrangement is disclosed in U.S. Pat. No. 4,953,680 wherein rotating gear typically includes a central bolt terminating in a hex-head that is engaged by a socket wrench for rotating the gear. The clutch adjuster is locked in position by a formed lock strap that prevents rotation of the head associated with the gear. The formed lock strap also works as a biasing member. The locking and unlocking of the head of the central bolt is done by pressing down the formed lock strap. Further a separate biasing member in the form of a coil spring may also be incorporated in between the head of the central bolt and above the central depressed area of the top plate. The clutch adjuster is designed to unlock by pressing the center bolt down at a reasonable force. Specifically, axial movement of the center bolt is necessary to perform the locking and unlocking of the clutch adjuster. Due to the dirty environment and the size of the ring to be rotated, the teeth of the adjusting ring and clutch adjuster can become frozen or locked. This increases substantially the force needed to axially move the center bolt to unlock the adjuster, and may make it practically impossible. Further the locking is “blind,” i.e., the locking surfaces are obscured from view. This leads to uncertainty as to whether locking has, in fact, occurred. If the clutch adjuster is not, in fact, locked into position, upon the first engagement of the clutch, the central bolt will rotate, and thereby clutch will go out of adjustment and thus the clutch will become inoperable.
The clutch adjuster such as disclosed in U.S. Pat. No. 6,974,013 has a specially designed top plate or bracket having a central depressed area between two L-shaped arms. The bracket is adapted to be secured to the clutch cover. The depressed portion of the bracket has an aperture for adopting a bolt having a head and a shaft. The shaft of the bolt has a rotary gear having teeth adapted to mesh with the teeth of an adjusting ring. The bracket further accommodates a rectangular locking member for selectively locking the head of the bolt and to prevent rotation of the bolt. The locking member is placed above the central depressed area of top plate or bracket and head of the bolt. Further a disc spring or a spring washer is accommodated below the locking member and above the central depressed area of the top plate or bracket. The spring biases the locking member towards the head of the bolt. The locking member prevents the rotation of the bolt, when in locking engagement with the head of the bolt so that the arms of the top plate or bracket substantially prevent rotation of the locking member. However the specially designed top plate or bracket having a centrally depressed area increases cost substantially and results in complex and heavy adjuster. Further the bracket having bends at four places posses a greater chance of failure because of increased stress at the curvatures. The locking member and the spring being above the top plate or bracket of the adjuster are susceptible to dirt and often get jammed over period of time.
Another clutch adjuster is disclosed in U.S. Pat. No. 5,320,205. The disclosed clutch adjuster has a specially designed bent top plate and a central bolt having a special hexagonal shape formed on its shaft. The central depressed area of the top plate has a corresponding female hexagonal groove which acts as a locking device for the central bolt. A biasing member is placed between the central depressed area of the top plate and the head of the central bolt. For adjusting clutch, the central bolt head is pressed down by an external force until the hexagonal shaped part comes out of engagement with the central depressed area of the top plate. A rotary gear also moves axially with the central bolt for adjusting the clutch. With the dirt and dust in the clutch during working, teeth of the rotary gear and the adjusting ring may gets jammed and may not permit their axial movement. Also the biasing member being above the top plate may get jammed due to dirt and dust.
The present invention is directed to overcoming one or more of the problems as set forth above.